Είναι σαφές ότι κανείς δεν μπορεί να δώσει μια εύκολη ή μονολεκτική απάντηση σε αυτό το ερώτημα, γιατί υπάρχουν αρκετοί και διαφορετικοί παράγοντες που επηρεάζουν την κάθε φωτοβολταϊκή εγκατάσταση, άλλοι λιγότερο και άλλοι περισσότερο (π.χ. ύψος ηλιοφάνειας, χωροταξικές ιδιαιτερότητες, μετεωρολογικές συνθήκες, κόστος, προσανατολισμός, σκιάσεις κλπ). Στη συνέχεια του άρθρου, θα κάνουμε μια προσπάθεια να περιγράψουμε συνοπτικά τα βασικά χαρακτηριστικά του κάθε τύπου ούτως ώστε να γίνουν όσο το δυνατόν πιο σαφείς οι διαφορές τους.
Πως κατασκευάζονται τα φωτοβολταϊκά πάνελ;
Το υλικό που χρησιμοποιείται περισσότερο για την κατασκευή φωτοβολταϊκών στοιχείων στη βιομηχανία είναι το πυρίτιο. Είναι ίσως και το μοναδικό υλικό που παράγεται με τόσο μαζικό τρόπο. Το πυρίτιο σήμερα, αποτελεί την πρώτη ύλη για το 90% της αγοράς των φωτοβολταϊκών (φωτογραφία 1).
Τα σημαντικότερα πλεονεκτήματα του πυριτίου είναι:
-Μπορεί να βρεθεί πάρα πολύ εύκολα στη φύση. Είναι το δεύτερο σε αφθονία υλικό που υπάρχει στον πλανήτη μετά το οξυγόνο.
-Μπορεί εύκολα να λιώσει και να μορφοποιηθεί.
-Οι ηλεκτρικές του ιδιότητες μπορούν να διατηρηθούν μέχρι και στους 125oC κάτι που επιτρέπει τη χρήση του πυριτίου σε ιδιαίτερα δύσκολες περιβαλλοντικές συνθήκες. Αυτός είναι και ο λόγος που τα φωτοβολταϊκά στοιχεία πυριτίου αντεπεξέρχονται σε ένα ιδιαίτερα ευρύ φάσμα θερμοκρασιών.
Το πυρίτιο, ανάλογα με την επεξεργασία του, δίνει μονοκρυσταλλικά, πολυκρυσταλλικά ή άμορφα υλικά, από τα οποία παράγονται τα φωτοβολταϊκά στοιχεία (κυψέλες).
Τα φωτοβολταϊκά πάνελ συνήθως αποτελούνται από:
-Ένα ηλιακό γυαλί με προ-τοποθετημένη την ειδικά επεξεργασμένη μεμβράνη προστασίας (EVA). Πρόκειται ουσιαστικά για ένα σκληρυσμένο, προεντεταμένο ηλιακό γυαλί.
-Ηλιακές φωτοβολταϊκές κυψέλες ενωμένες σε στοιχειοσειρές.
-Μία υαλώδη μεμβράνη ειδικής επεξεργασίας (EVA) καθώς και μια μονωτική μεμβράνη στην πίσω πλευρά. Και τα τρία παραπάνω στρώματα δημιουργούν ένα ανθεκτικό ελασματοποιημένο φύλλο, πολύ ανθεκτικό στις καιρικές συνθήκες, το οποίο τοποθετείται σε ένα σταθεροποιητικό πλαίσιο αλουμινίου και μια υποδοχή σύνδεσης (φωτογραφία 2).
Η αναφερόμενη «απόδοση» για κάθε τύπο πάνελ είναι ουσιαστικά το ποσοστό της ηλιακής ενέργειας που μετατρέπει σε ηλεκτρική ενέργεια. Ο βαθμός απόδοσης (efficiency) κυμαίνεται σήμερα από 6%-19%.
In this article, you will learn everything you need to know about the different types of solar panels for home use (mono-, polycrystalline and thin film).
Let’s start with the different types of solar panels currently on the market, list their benefits and downsides, and then look at a few typical scenarios where certain types would be the better than others (hopefully one of them resonates with you).
The term solar panels will be used to describe photovoltaic solar panels (the type that generates electricity), not solar thermal collectors.
CRYSTALLINE SILICON (C-SI)
Almost 90% of the World’s photovoltaics today are based on some variation of silicon. In 2011, about 95% of all shipments by U.S. manufacturers to the residential sector were crystalline silicon solar panels.
The silicon used in PV takes many forms. The main difference is the purity of the silicon.
But what does silicon purity really mean? The more perfectly aligned the silicon molecules are, the better the solar cell will be at converting solar energy (sunlight) into electricity (the photoelectric effect).
The efficiency of solar panels goes hand in hand with purity, but the processes used to enhance the purity of silicon are expensive. Efficiency should not be your primary concern. As you will later discover, cost-and space-efficiency are the determining factors for most people.
Compare Solar Panels
is the most comprehensive and up-to-date solar panel comparison service on the Internet. Compare the specifications of 10,000+ solar modules. Solar Cell Comparison Chart
provides a quick overview over the different cell types, their benefits and how they compare against each other.
Crystalline silicon forms the basis of mono- and polycrystalline silicon solar cells:
MONOCRYSTALLINE SILICON SOLAR CELLS
Solar cells made of monocrystalline silicon (mono-Si), also called single-crystalline silicon (single-crystal-Si), are quite easily recognizable by an external even coloring and uniform look, indicating high-purity silicon, as you can see on the picture below:
Monocrystalline solar cells are made out of silicon ingots, which are cylindrical in shape. To optimize performance and lower costs of a single monocrystalline solar cell, four sides are cut out of the cylindrical ingots to make silicon wafers, which is what gives monocrystalline solar panels their characteristic look.
A good way to separate mono- and polycrystalline solar panels is that polycrystalline solar cells look perfectly rectangular with no rounded edges.
- Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon. The efficiency rates of monocrystalline solar panels are typically 15-20%. SunPower produces the highest efficiency solar panels on the U.S. market today. Their E20 series provide panel conversion efficiencies of up to 20.1%.Update (April, 2013): SunPower has now released the X-series at a record-breaking efficiency of 21.5%. 
- Monocrystalline silicon solar panels are space-efficient. Since these solar panels yield the highest power outputs, they also require the least amount of space compared to any other types. Monocrystalline solar panels produce up to four times the amount of electricity as thin-film solar panels.
- Monocrystalline solar panels live the longest. Most solar panel manufacturers put a 25-year warranty on their monocrystalline solar panels.
- Tend to perform better than similarly rated polycrystalline solar panels at low-light conditions.
The efficiency of individual solar cells is higher than for entire solar panels/modules. For a complete overview over how the efficiency rates of the various solar cell technologies have advanced since 1975 check out Best Research-Cell Efficiencies (NREL)
. The efficiency rates in this article refer to solar panel/module efficiencies. Check out What Factors Determine Solar Panel Efficiency?
for more information on this subject.
- Monocrystalline solar panels are the most expensive. From a financial standpoint, a solar panel that is made of polycrystalline silicon (and in some cases thin-film) can be a better choice for some homeowners.
- If the solar panel is partially covered with shade, dirt or snow, the entire circuit can break down. Consider getting micro-inverters instead of central string inverters if you think coverage will be a problem. Micro-inverters will make sure that not the entire solar array is affected by shading issues with only one of the solar panels.
- The Czochralski process is used to produce monocrystalline silicon. It results in large cylindrical ingots. Four sides are cut out of the ingots to make silicon wafers. A significant amount of the original silicon ends up as waste.
- Monocrystalline solar panels tend to be more efficient in warm weather. Performance suffers as temperature goes up, but less so than polycrystalline solar panels. For most homeowners temperature is not a concern.
POLYCRYSTALLINE SILICON SOLAR CELLS
The first solar panels based on polycrystalline silicon, which also is known as polysilicon (p-Si) and multi-crystalline silicon (mc-Si), were introduced to the market in 1981. Unlike monocrystalline-based solar panels, polycrystalline solar panels do not require the Czochralski process. Raw silicon is melted and poured into a square mold, which is cooled and cut into perfectly square wafers.
- The process used to make polycrystalline silicon is simpler and cost less. The amount of waste silicon is less compared to monocrystalline.
- Polycrystalline solar panels tend to have slightly lower heat tolerance than monocrystalline solar panels. This technically means that they perform slightly worse than monocrystalline solar panels in high temperatures. Heat can affect the performance of solar panels and shorten their lifespans. However, this effect is minor, and most homeowners do not need to take it into account.
- The efficiency of polycrystalline-based solar panels is typically 13-16%. Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels.
- Lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of monocrystalline silicon. However, this does not mean every monocrystalline solar panel perform better than those based on polycrystalline silicon.
- Monocrystalline and thin-film solar panels tend to be more aesthetically pleasing since they have a more uniform look compared to the speckled blue color of polycrystalline silicon.
STRING RIBBON SOLAR CELLS
String Ribbon solar panels are also made out of polycrystalline silicon. String Ribbon is the name of a manufacturing technology that produces a form of polycrystalline silicon. Temperature-resistant wires are pulled through molten silicon, which results in very thin silicon ribbons. Solar panels made with this technology looks similar to traditional polycrystalline solar panels.
Evergreen Solar was the main manufacturer of solar panels using the String Ribbon technology. The company is now bankrupt, rendering the future for String Ribbon solar panels unclear.
- The manufacturing of String Ribbon solar panels only uses half the amount silicon as monocrystalline manufacturing. This contributes to lower costs.
- The manufacturing of String Ribbon solar panels is significantly more energy extensive and more costly.
- Efficiency is at best on par with the low-end polycrystalline solar panels at around 13-14%. In research laboratories, researchers have pushed the efficiency of String Ribbon solar cells as high as 18.3%.
- String Ribbon solar panels have the lowest space-efficiency of any of the main types of crystalline-based solar panels.
THIN-FILM SOLAR CELLS (TFSC)
Depositing one or several thin layers of photovoltaic material onto a substrate is the basic gist of how thin-film solar cells are manufactured. They are also known as thin-film photovoltaic cells (TFPV). The different types of thin-film solar cells can be categorized by which photovoltaic material is deposited onto the substrate:
- Amorphous silicon (a-Si)
- Cadmium telluride (CdTe)
- Copper indium gallium selenide (CIS/CIGS)
- Organic photovoltaic cells (OPC)
Depending on the technology, thin-film module prototypes have reached efficiencies between 7–13% and production modules operate at about 9%. Future module efficiencies are expected to climb close to the about 10–16%.
The market for thin-film PV grew at a 60% annual rate from 2002 to 2007. In 2011, close to 5% of U.S. photovoltaic module shipments to the residential sector were based on thin-film.
- Mass-production is simple. This makes them and potentially cheaper to manufacture than crystalline-based solar cells.
- Their homogenous appearance makes them look more appealing.
- Can be made flexible, which opens up many new potential applications.
- High temperatures and shading have less impact on solar panel performance.
- In situations where space is not an issue, thin-film solar panels can make sense.
- Thin-film solar panels are in general not very useful for in most residential situations.They are cheap, but they also require a lot of space. SunPower`s monocrystalline solar panels produce up to four times the amount of electricity as thin-film solar panels for the same amount of space.
- Low space-efficiency also means that the costs of PV-equipment (e.g. support structures and cables) will increase.
- Thin-film solar panels tend to degrade faster than mono- and polycrystalline solar panels, which is why they typically come with a shorter warranty.
Solar panels based on amorphous silicon, cadmium telluride and copper indium gallium selenide are currently the only thin-film technologies that are commercially available on the market:
AMORPHOUS SILICON (A-SI) SOLAR CELLS
Because the output of electrical power is low, solar cells based on amorphous silicon have traditionally only been used for small-scale applications such as in pocket calculators. However, recent innovations have made them more attractive for some large-scale applications too.
With a manufacturing technique called “stacking”, several layers of amorphous silicon solar cells can be combined, which results in higher efficiency rates (typically around 6-8%).
Only 1% of the silicon used in crystalline silicon solar cells is required in amorphous silicon solar cells. On the other hand, stacking is expensive.
CADMIUM TELLURIDE (CDTE) SOLAR CELLS
Cadmium telluride is the only thin-film solar panel technology that has surpassed the cost-efficiency of crystalline silicon solar panels in a significant portion of the market (multi-kilowatt systems).
The efficiency of solar panels based on cadmium telluride usually operates in the range 9-11%.
First Solar has installed over 5 gigawatts (GW) of cadmium telluride thin-film solar panels worldwide. The same company holds the world record for CdTe PV module efficiency of 14.4%.
COPPER INDIUM GALLIUM SELENIDE (CIS/CIGS) SOLAR CELLS
Compared to the other thin-film technologies above, CIGS solar cells have showed the most potential in terms of efficiency. These solar cells contain less amounts of the toxic material cadmium that is found in CdTe solar cells. Commercial production of flexible CIGS solar panels was started in Germany in 2011.
The efficiency rates for CIGS solar panels typically operate in the range 10-12 %.
Many thin-film solar cell types are still early in the research and testing stages. Some of them have enormous potential, and we will likely see more of them in the future.
BUILDING-INTEGRATED PHOTOVOLTAICS (BIPV)
Lastly, we`ll briefly touch on the subject of building integrated photovoltaics. Rather than an individual type of solar cell technology, building integrated photovoltaics have several subtypes (or different methods of integration), which can be based on both crystalline-based and thin-film solar cells.
Building integrated photovoltaics can be facades, roofs, windows, walls and many other things that is combined with photovoltaic material. If you have the extra money and want to seemlessly integrate photovoltaics with the rest of your home, you should look up building integrated photovoltaics. For most homeowners it`s simply way too expensive.
This article covered the advantages and disadvantages of different solar panel types. If you want to learn more solar power in general, go to Solar Energy Pros and Cons
BEST SOLAR PANEL TYPE FOR HOME USE
Having your particular situation evaluated by an expert would be the best way to find out what solar panel type would be best for your household. Here are some of the typical scenarios we see:
For those who don’t have enough space for thin-film solar panels (the majority of us), or if you want to limit the amount of space their PV-system takes up, crystalline-based solar panels are your best choice (and they would likely be the your best choice even if you had the extra space). There are not a whole lot of solar installers and providers that offer thin-film solar panels for homeowners at this point.
You will have a choice of different solar panel sizes. The 180, 200 and 220-watt rated solar panels are usually physically the same size. They are manufactured exactly the same way, but under- or overperform when tested, hence ending up in different categories for power output. If size is important, you should go for the highest rated power output for a particular physical size.
Both mono- and polycrystalline solar panels are good choices and offer similar advantages. Even though polycrystalline solar panels tend to be less space-efficient and monocrystalline solar panels tend to produce more electrical power, this is not always the case. It would be nearly impossible to recommend one or the other by not examining the solar panels and your situation closer.
Monocrystalline solar panels are slightly more expensive, but also slightly more space-efficient. If you had one polycrystalline and one monocrystalline solar panel, both rated 220-watt, they would generate the same amount of electricity, but the one made of monocrystalline silicon would take up less space.
We always keep an up-to-date list over the most efficient solar panels on the market today: What are the Most Efficient Solar Panels?
If you want the lowest costs per rated power, or in other words, pay as little as possible for a certain amount of electricity, you should investigate if thin-film solar panels could in fact be a better choice than mono- or polycrystalline solar panels